There are many applications for which precise control over the amount and/or rate at which a fluid is dispensed by a pumping apparatus is necessary. In semiconductor processing, for example, it is important to control the amount and rate at which photochemicals, such as photoresist chemicals, are applied to a semiconductor wafer. The coatings applied to semiconductor wafers during processing typically require a flatness across the surface of the wafer that is measured in angstroms. The rates at which processing chemicals, such as photoresists chemicals, are applied to the wafer have to be controlled in order to ensure that the processing liquid is applied uniformly.
Many photochemicals used in the semiconductor industry today are very expensive, frequently costing as much as $1000 a liter. Therefore, it is preferable to ensure that a minimum but adequate amount of chemical is used and that the chemical is not damaged by the pumping apparatus. Current multiple stage pumps can cause sharp pressure spikes in the liquid. Such pressure spikes and subsequent drops in pressure may be damaging to the fluid (i.e., may change the physical characteristics of the fluid unfavorably). Additionally, pressure spikes can lead to built up fluid pressure that may cause a dispense pump to dispense more fluid than intended, or to introduce unfavorable dynamics into the dispense of the fluid.
Other conditions occurring within a multiple stage pump may also prevent proper dispense of chemical. These conditions, in the main, result from timing changes in the process. These timing changes may be intentional (e.g., recipe changes) or unintentional, for example, signal lag, etc.
When these conditions occur, the result can be an improper dispense of chemical. In some cases no chemical may be dispensed onto a wafer, while in other cases chemical may be non-uniformly distributed across the surface of the wafer. The wafer may then undergo one or more remaining steps of a manufacturing process, rendering the wafer unsuitable for use and resulting, eventually, in the wafer being discarded as scrap.
Exacerbating this problem is the fact that, in many cases, the scrap wafer may only be detected using some form of quality control procedure. Meanwhile, however, the condition that resulted in the improper dispense, and hence the scrap wafer, has persisted. Consequently, in the interim between when the first improper dispense, and the detection of the scrap wafer created by this improper dispense, many additional improper deposits have occurred on other wafers. These wafers must, in turn, also be discarded as scrap.
As can be seen, then, it is desirable to detect or confirm that a proper dispense has occurred. This confirmation has, in the past, been accomplished using a variety of techniques. The first of these involves utilizing a camera system at the dispense nozzle of a pump to confirm that a dispense has taken place. This solution is non-optimal however, as these camera systems are usually independent of the pump and thus must be separately installed and calibrated. Furthermore, in the vast majority of cases, these camera systems tend to be prohibitively expensive.
Another method involves the use of a flow meter in the fluid path of the pump to confirm a dispense. This method is also problematic. An additional component inserted into the flow path of the pump not only raises the cost of the pump itself but also increase the risk of contamination of the chemical as it flows through the pump.
Thus, as can be seen what is needed are methods and systems for confirming operations and actions of a pump which may quickly and accurately detect the proper completion of these operations and actions.